According to the Centers for Disease Control and Prevention (CDC) , over 50% of adults over the age of 18 had at least one alcoholic drink per month in 2010. Of course, many of those folks (myself included) drank much more than that, totaling $152 billion dollars in the US alone according to US Department of Agriculture (USDA). For context, that's about 10% of what Americans spent on all other food the same year.

Humans have been brewing alcoholic beverages from almost the moment we settled down and domesticated food crops - in fact, some have argued that beer was the whole reason we got domestic in the first place. Whatever the veracity of that claim, it's clear that we've been making and imbibing alcohol for at least the last 7,000 years. Inebriation is a staple of civilization.

With that in mind, I've decided to start a monthly series here at Food Matters that I'm calling "Friday Happy Hour," in which I'll delve into the science of alcohol production. And alcohol production is most definitely a science. From microbiology to metabolism to chemistry and engineering, making a safe and consistent batch of your favorite brew requires an enormous amount of experimentation and precision. Each month, I'll center the post on a particular type of beverage, and describe the science behind it. I'm mostly a craft beer drinker, but I'll try to branch out into wines and spirits as well. And perhaps my co-bloggers will take some stabs at this as well. Leave your suggestions in the comments!

To get started, despite my own flavor biases, I thought I should start with the most popular beer style in the US: American style Lagers. But before we get to the actual beer tasting, let's get some science out of the way.

How to make alcohol: Let yeast do the work!

I said above that humans have been making alcohol for at least 7,000 years, but this is a bit disingenuous. In reality, most of the work is done by these guys:

The budding yeast Saccharomyces cerevisiae (click for source)

Saccharomyces ceravesiae is a budding yeast responsible for many things, including beer, wine, bread, and the fact that the verb "to shmoo" is part of biological jargon. This yeast is a fungus and like us, it breaks down the chemical bonds in sugars and uses the energy released from this break-down in order to live. The first step in the break-down is called glycolysis, which is actually a long series of chemical reactions that split a simple sugar like glucose into two pieces, releasing a small amount of energy. Some of that energy is stored in a form that is readily usable by cells in a molecule called ATP. A bit more energy from glycolysis is stored in a molecule called NADH that's produced by reducing NAD+.

In the presence of oxygen, a great deal more energy can be extracted from that same molecule of glucose. The two halves resulting from glycolysis can be broken down further, ultimately producing carbon dioxide as a waste product, but the NADH created during glycolysis can also be oxidized back into NAD+ to get more usable ATP energy. Unfortunately, (or fortunately is you're a brewer), this process doesn't work without oxygen.

Under these conditions (called "anaerobic" conditions), NADH builds up, and the supply of NAD+ dwindles. Anaerobic metabolism poses a number of problems for cells. The first is that a lot of energy is left on the table - complete breakdown of glucose under aerobic metabolism yields over 15 times as much energy as glycolysis alone. Even more problematic, as the supply of NAD+ gets converted into NADH, cells can no longer eek out even the meager energy gains of glycolysis.

The later problem is solved by fermentation, in which NADH is converted back into NAD+ by reducing the halves of sugar created in glycolysis. This means that the energy stored by NADH is wasted - no ATP is created in this process - but if there's more sugar around, this at least allows glycolysis to continue.

The energy requirements for animal survival are much too high for this to be sustainable, which is why constantly breathing oxygen is vital, but sometimes our cells are a bit starved for oxygen and turn to fermentation to get a little extra boost. For instance, during exercise, muscles use up a great deal of energy, sometimes outpacing the ability of blood to carry sufficient oxygen to keep up. Animal fermentation produces lactic acid, which can build up in muscle tissue and cause the characteristic "burn" associated with extreme physical exertion.

Fermentation allows the cell to recover NAD+ needed in glycolysis, and produces lactate or ethanol as a waste product (click for source)

Yeast are a bit different. As single-celled organisms, they can survive quite happily without oxygen, and instead of lactic acid, they produce ethanol (alcohol) as a waste-product during fermentation. No one knows quite how people first made this happy discovery, but the consensus seems to be that it was entirely by accident. Maybe some malting barley was left in a barrel with the lid on and the yeast from the environment went to town. The people that drank the resulting broth would have discovered its magical properties and set out to replicate the process.

Whatever the original source of knowledge, brewers soon managed to control the process, but it wasn't until the mid 19th century that the role of microorganisms in brewing was understood. We now know that, in addition to the production of alcohol - the active ingredient as it were - different strains of yeast can also impart a number of other chemical compounds to beer that can have dramatic effects on the flavor. I'll go into a lot more detail on these points in future posts in this series, but for now, just take my word for it.

Americans are into bland beers (or at least, they have been)

Which brings me back to American style lagers. We're talking here about brands like Budweiser, Miller and Coors, the top selling (by volume) beers in the United States. Beer aficionados and connoisseurs typically look down on these brews for tasting bland, but that's no accident. Prohibition in the early 20th century tanked beer consumption and wiped out most American brewers. On the other side of the 21st amendment, the American beer palate was wiped out as well, and the beers that tended to do well had a very neutral flavor. Brewers specifically selected strains of yeast that didn't impart too many flavors to their beer, used recipes with low amounts of flavorful ingredients like hops, and used adjuncts like rice and corn, which have simple sugars that don't produce as many off-flavors as the more traditional malted barley when metabolized by the yeast.

Bud Light is actually the most sold beer brand in the US, but I couldn't bring myself to buy it - too many bad memories of college parties. Instead, I chose the non-light equivalent (still in the top 3), the self-styled "King of Beers."

The Review: Budweiser

A large can of Bud poured into a glass we stole from a local restaurant.

Budweiser is an old brand by US standards. The longest surviving brewery in the world is over 1,000 years old, but in the US, most breweries were wiped out by prohibition in the early 20th century. Anheuser-Busch, the brewery that originally produced Budwieser, was founded in the mid 19th century, and introduced this particular brand in 1876.

Anheuser-Busch mananged to scrape through prohibition by selling products related to brewing, like malt extracts and yeast, and managed to bounce back quickly after prohibition was repealed. Because they didn't have to start from scratch, they had a leg up and quickly became the most successful brewer in America.

To be honest, I don't think I've had Budweiser since I took a sip of my dad's when I was like 8 years old. As somewhat of a beer snob, I was expecting to hate it, but it actually wasn't that bad. It's not very complex (for reasons I mentioned above), but it's not unpleasant. The beer pours nicely with a decent head, though that bubbled away quickly. The color is pale, clear yellow. The smell is a bit unpleasant for me, but I suspect that's because of the sense-memory of cleaning up after parties (and the stale-beer smell). It's a bit sweet, a bit yeasty, but not much more to speak of.

The taste is surprisingly not-bad. I don't think I would ever choose this beer over other options, but it's crisp, clean and drinkable. Sort of boring, but hey, there's nothing wrong with that. Not much of a finish to speak of - a bit of a beery aftertaste, but it doesn't last long. Maybe it benefited from low expectations, but overall it was very OK.

I've started a beeradvocate profile and will try to start reviewing beers there, but I'm new to this part of it. If any of you are aficionados and want to point me towards your reviews and recommendations, please do so.

If you have ideas or suggestions for beverages to talk about, please let me know in the comments. For the month of October I'll be talking about (what else?) Oktoberfest!

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

Kevin Bonham

Kevin Bonham is a Curriculum Fellow in the Microbiology and Immunobiology department at Harvard Medical school. He received his PhD from Harvard, where he studied how the cells of the immune system detect the presence of infectious microbes. Find him on Google+, Reddit.

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